This invention relates to novel coated abrasives, and, in particular, to a lapping material in sheet form.
"Lapping", as the term is used in this specification, means working a particulate abrasive material against the surface of a workpiece until an exceedingly fine, mirror-like finish is imparted thereto. The objective sought is the attainment of a very smooth surface finish, while retaining a high degree of dimensional control, so that the resulting product will conform to very precise size standards. The lapping of surfaces from their original state to the final finish is a progressive operation, involving the use of a series of abrasives ranging from relatively coarse at the beginning through successively finer sizes to the end. The results secured depend upon a number of factors, such as the properties of the abrasive employed, the pressure with which the abrasive is forced against the workpiece, the pattern of movement preserved in the contact of the workpiece with the abrasive particles and other considerations.
The earliest methods of lapping employed particulate abrasive materials suspended in a liquid vehicle to form a slurry. The suspension was worked against the surface of the workpiece until the desired finish was attained. Examples of lapping methods employing abrasive slurries are described in U.S. Pat. Nos. 2,655,775; 4,059,929; 4,046,524; 4,246,003.
More recently, lapping materials in pad or sheet form have been developed. U.S. Pat. No. 4,288,233 describes lapping pads for ophthalmic lenses. While the lapping material of this invention is useful, the components thereof, i.e. diamonds, and the method of making it, i.e. metal plating, are expensive. Furthermore the lapping materials described therein are not flexible.
U.S. Pat. No. 4,255,164 discloses a glass fining sheet suited for finishing rough ground vitreous surfaces to provide a surface finish which may be readily polished comprising a flexible, conformable backing sheet bearing a microcellular abrasive granule-resin matrix which, under use conditions and in the presence of an aqueous flow, generates a fining slurry. The fining sheet is prepared by coating a flexible conformable backing sheet with a foamed liquid abrasive granule-resin coating composition comprised of liquid curable binder material, abrasive fining granules, and sufficient compatible solvent to provide a coatable composition. The coating provides a cellular layer which releases the fining abrasive granules at a controlled rate under use conditions. The released granules perform the actual abrading. The sheet of this patent appears to be another means of preparing a fining slurry.